1. Field of Invention
This invention relates to vertical strip indicators for the display of parameter values such as instantaneous values of aircraft engine characteristics and to the means for transmitting light from the illumination source to the visible face of the individual segments of which the vertical strip is composed.
2. Description of the Prior Art
In many fields of scientific and other endeavor it is necessary to measure continuously the value of certain characteristics such as pressure, temperature, force, etc. It is necessary to present these measurements by means of indicators to operators of the equipment to which the measurements pertain. Specifically in the case of aircraft it is most important that measurements of pressure, temperature, torque, and revolutions per minute of engines be presented to pilots and flight engineers instantly. In the past indicators used to present the information have been traditionally round with a clock-like dial showing the values attainable with a centrally pivoted needle or pointer to indicate the instantaneous value. Traditionally the dial face is black in color with white or fluorescent numerals and the pointer is white or fluorescent, the pointer being mounted one-eighth inch or more in front of the dial face to allow for pointer rotation.
Among the disadvantages inherent in the construction of the traditional indicators, two are most significant. First, the frontal area of the indicator is approximately 10 square inches when mounted on the aircraft cockpit panel which severely limits the number of indicators that can be mounted in the cramped cockpit space of modern aircraft. Secondly, parallax errors occur when the operator views the indicator from any angle other than exactly perpendicular. Parallax is described by Webster as "the apparent displacement of an object, as seen from two different points." In the particular case of an indicator which has its pointer mounted one-eighth inch or more from the dial face, the viewer sees the pointer indicating an incorrect value when the viewer views the indicator from any position other than exactly in front of the indicator, the incorrectness of the value increasing as the viewer is positioned further from the perpendicular.
Three previous inventions have been dedicated to indicators:
U.S. Pat. No. 3,726,250 INDICATOR PA1 U.S. Pat. No. 3,809,877 INDICATOR POINTER PA1 U.S. Pat. No. 3,885,230 SYSTEM FOR IMPROVING THE RELIABILITY OF INDICATOR ARRANGEMENTS
U.S. Pat. No. 3,726,250 teaches the replacement of the usual pointer in an indicator device by a path of moving light comprising a plurality of individually illuminable elements arranged in a circular pattern to follow the same configuration as did the numerical values when the indicator device was fitted with a pointer.
U.S. Pat. No. 3,809,877 teaches the reconfiguring of the path of moving light of U.S. Pat. No. 3,726,250 from its original circular shape to a vertical straight line which gives the indicator a thermometer-like appearance instead of the bulky traditional round hand-and-dial shape thus saving considerable space. U.S. Pat. No. 3,809,877 further teaches the use of individual incandescent light bulbs in intimate contact with the back of an opaque plate to provide individually illuminable elements, and further teaches that the individually illuminable elements are illuminated and extinguished in accordance with activation by logic circuitry which is in turn activated by the instantaneous value of the characteristic being measured.
U.S. Pat. No. 3,885,230 teaches the use of a plurality of separate power supplies for energizing the individually illuminable elements to prevent loss of indication in the event of a power supply failure.